3.3.1. Effect of the pH of the ammonia buffer
The influence of the pH on this system was investigated in pH
range of 6.0–11.0 (Fig. 3a). At pH lower than 8, the DI decreased
because the S2O3
2 was not stable and broke down into sulfate,
sulfide, sulfite tetrathionate, trithionate, polythionates and polysulfides
[31]. However, in the pH range of 9–12, the complex Cu
(NH3)4
2+ concentration increased with increasing NH3 concentration,
enabling the oxidation of AgNPls by Cu(NH3)4
2+. The intensity
color of modified AgNPls was almost constant above pH 11 in the
presence Cu2+. Therefore, pH 11 was selected as the optimal value
for all experiment.